The yellow stem borer (YSB) Scirpophaga incertulas Walker is a major and ubiquitous rice pest of either deep/semideep or irrigated rice. This species is dominant among the pyralids. A severe drought during the 2002 wet season (WS) (446.5 mm rainfall vs 1,200 mm average) drastically reduced the total adult moth population. From July to September, light trap collections decreased by 93.7%. In spite of these conditions, the semideepwater (SDW) entries showed heavy white ear infestation. We examined the reasons for these variations at the NDUAT research station.